Analytical signal as a tool for studying solar p-modes

A technique for analyzing periodic processes based on the introduction of an analytical signal is described. This technique allows the instantaneous frequency, amplitude, and phase of oscillations to be obtained. The data on solar brightness fluctuations collected with the DIFOS multichannel photometer onboard the CORONAS-F satellite are processed. The p-mode spectral lines are broadened mainly by amplitude fluctuations, while the frequency stability appears to be high (similar to 10(-4)). A method for separating signals with close frequencies is developed. The p-mode with l = 0 and n = 21 is Used as all example to show that the separation of signals with close frequencies is possible when the conventional spectral methods, are inefficient. Analysis of the phase shifts between the oscillations Observed in various Optical channels of the DIFOS photometer has revealed that the five-minute oscillations travel from file upper and deep photospheric layers toward the middle photospheric layers. This effect directly proves that the evanescent p-modes in the photosphere are nonadiabatic.